If you ever find yourself with a locked Yahoo account, it's likely due to multiple incorrect password attempts.
As a security measure, Yahoo's email and chat client servers automatically lock your account to prevent unauthorized access after there have been multiple invalid password entries.
The ID Lock security measure safeguards a Yahoo account from unauthorized users who try to access your account without permission.Cause
After multiple incorrect password entries to a Yahoo account, the server automatically sets a lock on it.
This happens because every time a Yahoo Account holder logs into his account, he's logged in with a cookie.
A cookie is an information packet that proves you are the valid account holder.
However, when a person tries to access an account with many failed attempts, the cookies expires, triggering the ID lock on the account.
A Yahoo account holder must wait up to 24 hours before accessing the account again.
The lock on the account expires within 24 hours from the time the account was locked.
Unlock Using Another Server
Since Yahoo! has many servers around the world, a user can log into his account by visiting a different Yahoo server address. (See Below.)
Copy and paste a Yahoo! server URL into the address bar of your Internet browser to access the website.
Enter the Yahoo! ID and password in their respective fields, and click on "Log in" to access your yahoo account.
Avoid Yahoo Account Locks
To prevent future Yahoo! account locks, a user should limit the number of times he tries to enter a password.
If an account holder has forgotten his password, he should use the "Forgot Passsword" feature to reset the password.